Pyrogallol is a useful compound suitable for use as photographic and dyeing industries or an intermediate in synthesis of organic chemicals. It is now being produced by thermal decarboxylation of gallic acid which is obtained from naturally occurring materials, and thus pyrogallol is expensive and its supply and application are limited. In view of the above, in order to obtain pyrogallol on a large scale at a low cost, the synthesis of pyrogallol from a cheap chemical compounds has been desired.
Production of phenols by dehydrogenation of a cyclohexanols has already been known. For example, "Doklady Akademii Nauk. SSSR. 185, 145 (1969)" teaches production of catechol by dehydrogenation of cyclohexane-1,2-diol and "Doklady Akademii Nauk. SSSR, 198, 1354 (1971)" discloses production of pyrogallol by dehydrogenation of cyclohexane-1,2,3-triol. Both processes employ a gas phase dehydrogenation reaction in which starting material is contacted with a catalyst system comprising metallic palladium and potassium carbonate supported on activated carbon at 300.degree. C. in a hydrogen stream.
We have examined the procedures disclosed in the literature above and found that cyclohexane-1,2-diol can successfully be produced but dehydrogenation of cyclohexane-1,2,3-triol results in mainly catechol and the selectivity of pyrogallol is very low. In order to improve the selectivity of pyrogallol in such dehydrogenation, we have conducted intensive studies and have found that if the reaction is carried out in a stream of an inert gas such as nitrogen, the selectivity of pyrogallol can be increased. This invention is conceived on the basis of this knowledge.